The present invention relates generally to an electric wire connecting device and, more specifically, to a wire connecting device used for connecting electric wires to a printed circuit board that is provided in an electronic apparatus such as a sequencer.
A technique of connecting an electric wire to a printed circuit board is known in which the wire is wound on the shank of a screw and, the screw is then screwed into a hole in a circuit board such that the wire is held between the bearing surface of the head of the screw and the surface of the circuit board. In this cases there may occur a phenomenon that during screwing, the wire is dragged as the screw is rotated. There is the possibility that if part of the wire being dragged is sticking out of the screw and some conductor exists in the vicinity of the screw, the wire may contact the conductor to cause short-circuiting, or the movement of the wire may damage the conductor and its connection to the circuit board.
As a countermeasure against this problem, Japanese Patent Laid-Open No. 268898/2000 discloses a technique of using a cam instead of a screw. A screw is used in this technique to advance the cam close to the wire and this advancement causes the cam to press against the wire as the screw is rotated further; the screw does not serve to directly connect the wire to the circuit board. This type of cam mechanism is used in a wire connecting device that is incorporated in an electronic apparatus as part of it.
The wire connecting device disclosed in the above publication has a housing as an outer body, a wire insertion hole through which to introduce an electric wire into the housing, a cam for pressing the wire that has been introduced while being guided by the wire insertion hole, a screw for causing the cam to function as means for pressing the wire, a manipulation hole into which a driver for rotating the screw is to be inserted, and a terminal to be joined to a circuit board of an electronic apparatus.
If the screw is rotated by inserting a driver through the manipulation hole after the wire has been inserted into the housing through the wire insertion hole, the screw advances or retreats in accordance with its rotation direction.
If the screw is rotated in the advancing direction, the screw contacts the cam in due course. If the screw is rotated further in the same direction, the wire is pressed by the cam. The wire is pressed by the cam at a portion of the terminal to be connected to the circuit board. As a result, the wire is electrically connected to the circuit board via the terminal.
Incidentally, in the technique described in the above publication, the cam is free to rotate when the screw is loose, that is, in the case that the cam is not pressed by the cam ,taking example, before the wire is connected to the circuit board). If in this state the connecting device is moved, or its orientation is changed or reversed to attach it to the electronic apparatus, the cam may rotate about a cam shaft due to its own weight. As a result, the cam may hit the walls etc. of the connecting device, whereby the cam or housing is damaged or sound is generated.
If the screw becomes loose and the cam rotates due to its own weight, the wire insertion hole may be shut by the cam, in which case the operator may not be able to insert into the connecting device, a necessary and sufficient length of the wire.
However, it is difficult to judged, from the outside, whether the wire insertion hole is shut by the cam. Therefore, if the operator inserts the wire into the insertion hole without knowing that the insertion hole is shut by the cam, the advance of the wire (a stranded wire or thin wires constituting it) is obstructed, making it difficult to insert the wire further or possibly unraveling the strands at the end of the wire.
The present invention provides the following measures to solve the above technical problems.
In the invention, rotation of a cam due to its own weight is prevented. To this end, the rotation of the cam is restricted by combining the cam with a slider that makes a go-movement or a return movement in accordance with the rotation direction of a screw.
More specifically, a wire connecting device according to the invention comprises a housing as an outer body; a screw that can rotate clockwise or counterclockwise about a rotation axis at a prescribed position in the housing while is prevented from moving in an axial direction; a slider that is threadedly engaged with the screw and makes a go-movement or a return-movement in accordance with a rotation direction of the screw; a guide hole through which to introduce an electric wire into the housing; and a cam that is in contact with a go-side surface or a return-side surface of the slider, rotates clockwise or counterclockwise in accordance with a movement direction of the slider, and presses the electric wire at a prescribed rotation position.
In the wire connecting device according to the invention having the above configuration, as the screw is rotated, the slider makes a go-movement or a return-movement in accordance with the rotation direction of the screw while friction occurs between the threadedly engaged portions of the screw and the slider.
The cam is in contact with the slider an rotates clockwise or counterclockwise in accordance with the movement direction of the slider. In other words, the cam does not rotate unless the slider is moved.
However, as described above, frictional drag occurs between the threadedly engaged portions of the screw and the slider. Therefore, to move the slider, external force that is stronger than the frictional drag should be exerted on the slider. The cam that is in contact with the slider does not rotate unless the slider is moved. That is, the cam does not rotate unless external force acting on the slider is stronger than the frictional drag. It can be said that the rotation of the cam is restricted by the slider.
Rotating the screw with a driver is not the only cause of external force that acts on the slider; there may occur a case that the cam exerts external force on the slider. For example, the weight of the cam itself may cause external force. In this case, the slider is moved if the force due to the weight of the cam itself is stronger than the frictional drag between the threadedly engaged portions of the screw and the slider.
There may occur a case that the guide hole through which to introduce the wire into the housing is shut by the cam. If the wire is inserted into the guide hole in this state, the advance of the wire is obstructed as described above.
Therefore, the frictional drag between the threadedly engaged portions of the screw and the slider should be sufficiently strong so as to prevent an event that the weight of the cam itself overcomes the frictional drag between the threadedly engaged portions of the screw and the slider and the cam shuts the guide hole undesirably. That is, it is desirable that the frictional drag that occurs between the threadedly engaged portions be set strong enough to prevent movement of the slider even if force due to the weight of the cam itself acts on the slider.
This measure prevents the cam from moving undesirably, and hence the cam can be prevented from hitting the walls or the constituent parts of the wire connecting device. Further, there does not occur a phenomenon that the cam shuts the wire insertion hole. Therefore, even if the wire is inserted into the wire insertion hole without checking whether it is shut by the cam, the advance of the wire (a stranded wire or thin wires constituting it) is not obstructed. This effectively prevents a phenomenon that it is difficult to insert the wire into the insertion hole or a stranded wire is unraveled.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.